Animals have diversified into a bewildering variety of morphological forms exploiting a complex configuration of trophic niches. Their morphological diversity is widely used as an index of ecosystem function, but the extent to which animal traits predict trophic niches and associated ecological processes is unclear. Here we use the measurements of nine key morphological traits for >99% bird species to show that avian trophic diversity is described by a trait space with four dimensions. The position of species within this space maps with 70–85% accuracy onto major niche axes, including trophic level, dietary resource type and finer-scale variation in foraging behaviour. Phylogenetic analyses reveal that these form–function associations reflect convergence towards predictable trait combinations, indicating that morphological variation is organized into a limited set of dimensions by evolutionary adaptation. Our results establish the minimum dimensionality required for avian functional traits to predict subtle variation in trophic niches and provide a global framework for exploring the origin, function and conservation of bird diversity.

动物已经利用复杂的营养生态位结构多样化，形成令人眼花缭乱的各种形态。它们的形态多样性被广泛用作生态系统功能的指标，但动物性状在多大程度上预测营养生态位和相关的生态过程尚不清楚。在这里，我们使用对 >99% 鸟类物种的九个关键形态特征的测量来表明鸟类营养多样性是由具有四个维度的特征空间描述的。该空间内物种的位置以 70-85% 的准确度映射到主要生态位轴，包括营养水平、饮食资源类型和觅食行为的更精细尺度变化。系统发育分析表明，这些形式-功能关联反映了向可预测性状组合的趋同，表明形态变异通过进化适应被组织成一组有限的维度。我们的结果确定了鸟类功能特征所需的最小维度，以预测营养生态位的细微变化，并为探索鸟类多样性的起源、功能和保护提供了一个全球框架。